Re: [PATCH] drivers/ata: Add the SW NCQ support to sata_nv for MCP51/MCP55/MCP61

Hi,

Jeff Garzik írta:> Alan Cox wrote:>>> That shouldn't be a problem, libata default DMA mask is 32 bits >>> (which isn't overridden with this controller) and so the block layer >>> will bounce any data being read/written above that point with IOMMU >>> or swiotlb. The comment is a bit unnecessarily scary.>>>> Adding a BUG_ON for this would be wise. Its trivial to check and a BUG>> rather than corruption if this assumption ever changes would be far>> preferable>> The default DMA mask -everywhere- is 32 bits.>> A lot of code will break if this assumption ever changes, not just > libata.>> Jeff

thanks for clarifying this.

I tested the effect of this patch on 2.6.22-rc2 + CFS-v13with the current CVS version of PostgreSQL 8.3devel.pgbench with 25 clients and some large number oftransactions to make the result stable showed substantialincrease in throughput. Without NCQ, I got around 446 tps,with NCQ I got around 680 via local TCP connection.Previously, I got this level of performance only overlocal unix socket and smaller number of simultaneous clients.The disk is Seagate 320GB (ST3320620AS).